The engine immobiliser system is designed to prevent the vehicle from being stolen. This system uses a transponder key ecu that stores the key codes of authorized ignition keys. If an attempt is made to start the engine using an unauthorized key, the ecu sends a signal to the ecm to prohibit fuel delivery and ignition, effectively disabling the engine.

The transponder key coil receives this signal, the transponder key amplifier amplifies it, and then the signal is transmitted to the ecu. The ecu matches the key's id code with the vehicle's id code, which was previously registered in the ecu and then communicates the results to the ecm using sfi communication.
Engine immobiliser system
How to proceed with troubleshootingInstallation
Install engine coolant temperature
sensor
Install a new gasket onto the sensor.
Using sst, install the sensor.
Sst 09817-33190
torque: 19.6 N*m (200 kgf*cm, 14 ft.*Lbf)
Connect the sensor connector.
Install air cleaner case (see page es-431)
Install air cleaner cap ( ...
Removal
Hint:
Use the same procedures for the rh side and lh side.
The procedures listed below are for the lh side.
Disconnect cable from negative battery
terminal
Caution:
Wait at least 90 seconds after disconnecting the
cable from the negative (-) battery terminal to
prevent airbag and ...
On-vehicle inspection
Check ignition coil assembly and perform spark test
Notice:
in this section, the terms "cold" and "hot" refer to
the temperature of the coils. "Cold" means
approximately -10 to 50°c (14 to 122°f). "Hot" means
approximately 50 to 100°c (122 to 212 ...